/*
 * Copyright 2017 Eric.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package varcode.translate;

public enum UnescapeJavaString
{
    ;

    /**
     * Copied from stack Overflow 
     * 
     * Unescapes a string that contains standard Java escape sequences.
     * <ul>
     * <li><strong>&#92;b &#92;f &#92;n &#92;r &#92;t &#92;" &#92;'</strong> :
     * BS, FF, NL, CR, TAB, double and single quote.</li>
     * <li><strong>&#92;X &#92;XX &#92;XXX</strong> : Octal character
     * specification (0 - 377, 0x00 - 0xFF).</li>
     * <li><strong>&#92;uXXXX</strong> : Hexadecimal based Unicode character.</li>
     * </ul>
     * 
     * @param st A string optionally containing standard java escape sequences.
     * @return The translated string.
     */
    public static String unescapeJavaString(String st) {

        StringBuilder sb = new StringBuilder(st.length());

        for (int i = 0; i < st.length(); i++) {
            char ch = st.charAt(i);
            if (ch == '\\') {
                char nextChar = (i == st.length() - 1) ? '\\' : st
                        .charAt(i + 1);
                // Octal escape?
                if (nextChar >= '0' && nextChar <= '7') {
                    String code = "" + nextChar;
                    i++;
                    if ((i < st.length() - 1) && st.charAt(i + 1) >= '0'
                            && st.charAt(i + 1) <= '7') {
                        code += st.charAt(i + 1);
                        i++;
                        if ((i < st.length() - 1) && st.charAt(i + 1) >= '0'
                                && st.charAt(i + 1) <= '7') {
                            code += st.charAt(i + 1);
                            i++;
                        }
                    }
                    sb.append((char) Integer.parseInt(code, 8));
                    continue;
                }
                switch (nextChar) {
                case '\\':
                    ch = '\\';
                    break;
                case 'b':
                    ch = '\b';
                    break;
                case 'f':
                    ch = '\f';
                    break;
                case 'n':
                    ch = '\n';
                    break;
                case 'r':
                    ch = '\r';
                    break;
                case 't':
                    ch = '\t';
                    break;
                case '\"':
                    ch = '\"';
                    break;
                case '\'':
                    ch = '\'';
                    break;
                // Hex Unicode: u????
                case 'u':
                    if (i >= st.length() - 5) {
                        ch = 'u';
                        break;
                    }
                    int code = Integer.parseInt(
                            "" + st.charAt(i + 2) + st.charAt(i + 3)
                                    + st.charAt(i + 4) + st.charAt(i + 5), 16);
                    sb.append(Character.toChars(code));
                    i += 5;
                    continue;
                }
                i++;
            }
            sb.append(ch);
        }
        return sb.toString();
    }
}
